1. Field of the Invention
The present invention relates to a lubricating oil composition that displays excellent thermal stability and lubrication properties, does not damage members used in working machinery, and is ideal for use in high-temperature environments.
The present invention relates particularly to a lubricating oil composition that is ideal as a chain lubricant for a tenter or the like.
2. Description of Related Art
Lubricating oils containing a polyolester based oil as the base oil display comparatively long hardening times (the length of time required for loss of fluidity) and low evaporation loss, and consequently offer excellent thermal stability. As a result, these types of lubricating oils have been widely commercialized as high-temperature lubricating oils, in lubricants for tenters used for the transverse stretching of resin films such as polypropylene (PP), polyethylene terephthalate (PET), polyamide (PA), or polyethylene (PE), or woven fabric, nonwoven fabric, building material, or the like in an open system at a temperature of approximately 200° C.
However, many of these lubricating oils generate large quantities of oxidation polymers and sludge, meaning they are not entirely suitable for practical application. In contrast, those lubricating oils which are deemed to suffer minimal sludge generation tend to have shorter hardening times, and larger levels of evaporation loss, meaning their inherent lubrication properties are inferior.
Furthermore, amongst high-temperature lubricating oils containing a base oil as described above, the addition of a phosphorus based compound or a sulfur based compound of a lubricant as an extreme pressure agent or an anti-wear agent is a common technique used to impart more favorable lubrication characteristics (for example, see Japanese Unexamined Patent Application, First Publication No. 2000-129279 and Japanese Unexamined Patent Application, First Publication No. 2001-303086). However, even lubricating oils containing these conventional additives can suffer problems during practical application. For example, under working machinery conditions, these additives can form secondary products that can cause blockages within the oil supply lines, or products generated by the decomposition of these additives can cause elution of those members within the machinery formed from silicone rubber or the like. (Note, in this description, the softening and deterioration of silicone based rubbers such as vinyl methyl silicone (VMQ) caused by a reduction in the molecular weight resulting from cleavage of the principal chain is referred to as “elution.”)
Accordingly, a lubricating oil that displays favorable high-temperature stability with no loss of lubrication properties, and does not effect the members used in working machinery, even when used in high-temperature open systems such as tenters, has been eagerly sought.